External power for the HP48GX

In this page I descrive how to use and modify the HP48G/GX for use with and external power suplly, without damag your calculator ( only and small hold in the IR cover ;-) !!!!

* Pardon for my english, it isn't my native lenguage.
If you read this and found any wrong word, expresion ... please email me at cvag@tinet.fut.es ;-) *

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It is based in my own experience, and I don't give any warranty, if you damage your HP.


Comments: I use my HP48GX for more than a year with the external power supply, and I don't have any problem with this, and I have'nt needed to change the batterys pile of the HP from then. Although I use the HP every day 2 or 3 hours in the university and at home, and I use many the connection with the PC.

Working: When you use the HP with no power supply connector then the HP work with the batterys, and when you conect the external power supply the HP works with it.

The External power supply: I construct my own external power supply, because I think that the external power supply that they are sold in the market, are not very stable, and the calculator is quite expensive ;-).

1.- Do the external powe supply, with the next next electronic circuit:

The C capacitator is in order to filter the interferences, and it has to be small. I use and 100 nF Capacitator.

2.- Put the male connector in the 4.4V output.

3.- Prove that the source in order to assure that it has 4.4 V.

Connections in the HP: Here I explain how modify the HP in order to use the external power for the HP48GX calculator.
( In the HP48G you need to do a hold inside the IR cover for put the connector and for pass the wires ).

1.- Cut the two small plates with the measure of the connector of the HP ( the connectors of the positive pole of the batterys ).

2.- Isolate the two plates with the isolated paper, and glue there.

|#|      # : Isolated paper.
|#|      | : Thin plates.
3.- Put it between the HP positive pole of the HP and the positive pole of the batterys.
( Probably you will need to narrow the positive pole of the HP with a nipper ).

4.- Solder a wire in each plate. ( 2 wires )

5.- Pass the fishing thread into the small hold of the HP have in the left of the batery space, to and small hold in the ramcard space.
When you do this pass the 2 wires into the place of the fishing thread.

6.- Do the same with one wire in the right of the HP. And solder it to the negative pole of the HP.

7.- With a cutter file the guides of the battery cover.

8.- File the female connector so that it adapt to the IR cover.
You need to use a plastic and small connector, with a switch in it.
If you use and small connector and file it, posible you can use a RAMCARD in slot 2 !!!

9.- Do a Hold in the IR cover. When you do this, think that the female connector has to fit inside the HP.

10.- Solder the wires in the female connector as it are in next picture.
When you do this, check that the switch of the connector continues working: ( it is possible that it have been solded for the heat, if it occur connect and disconnect the male connector several times and it is possible then it works ).

11.- Glue the female connector in the IR cover.

12.- Prove the HP with the external power supply and enjoy it !!!!!!!!!!

Using the external power with the HP: To finish some advice in order to use the external power with the HP:

- When you connect or disconnect the male connector OFF the HP.
- If you disconnect the external power, first disconnect there from the HP.
- The first days, when you disconnect de male connector, check that it really close the switch of the connector. ( otherwise you can lose the memory of the HP ).
- ....

More: If you have any question or any comment send me an email at cvag@tinet.fut.es

Carles Albert Vallvè Guionnet
Email: cvag@tinet.fut.es
ICQ: 7734313
Home Page: http://www.fut.es/~mpga/ ( it was in Catalan ).